1. Field of the Invention
The present invention relates to a paper floating detection apparatus and to an inkjet recording apparatus, and more particularly to a paper floating detection apparatus and an inkjet recording apparatus, allowing the detection height of floating paper to be varied.
2. Description of the Related Art
In an inkjet recording apparatus, a prescribed image is recorded on a recording surface of paper by ejecting ink droplets from an inkjet head onto paper which is conveyed along a predetermined conveyance path. In an inkjet recording apparatus of this kind, if the conveyed paper floats up from the conveyance surface, then there are possibilities that the distance from the nozzle surface of the head to the recording surface of the paper (the throw distance) changes, the recording quality declines, the paper rubs against the nozzle surface of the head and the nozzle surface becomes damaged. Consequently, in an inkjet recording apparatus, a paper floating detection apparatus is disposed in the paper conveyance path and if floating of a specified value or more is detected, then processing, such as halting conveyance, or the like, is implemented.
In general, floating up of paper has been detected by disposing a light emitting unit and a light reception unit in mutually opposing fashion across the paper conveyance path, emitting a detection beam from the light emitting unit toward the light reception unit in a position at a predetermined height from the conveyance surface, and detecting whether or not the detection beam is received. In other words, when floating of the paper occurs, the paper shields reception of the detection beam, and hence the presence or absence of floating of the paper is judged on this basis (see, for example, Japanese Patent Application Publication No. 2007-76109 and Japanese Patent Application Publication No. 2007-98650).
Papers which are recorded by an inkjet recording apparatus include papers of various different thicknesses. Therefore, if the thickness of the paper used has changed, it is necessary to change the floating detection height in accordance with this paper thickness.
Japanese Patent Application Publication No. 2004-299155 proposes technology in which a light emitting unit and a light reception unit are provided on a member that is raised and lowered together with an inkjet head, and a floating detection height is changed in accordance with the raising or lowering of the inkjet head.
However, in the technology described in Japanese Patent Application Publication No. 2004-299155, there is a possibility that fine adjustment is difficult due to the composition which alters the detection height by raising and lowering the inkjet head.
Furthermore, if the inkjet head is twisted, then positional displacement occurs between the light emitting unit and the light reception unit, and hence there is a possibility that the detection accuracy falls.
Moreover, in an apparatus which carries out maintenance by moving an inkjet head periodically to a maintenance unit, discrepancy may occur in the detection height each time the inkjet head is moved, and hence there is a possibility that highly accurate detection cannot be carried out in a stable fashion.
Furthermore, a light emitting unit and a light reception unit are provided below the inkjet head, and therefore when the inkjet head is withdrawn, the withdrawal amount is required to be made large and hence there is a possibility that the apparatus becomes large in size.